Embodiments described herein relate generally to electrochemical cells having semi-solid electrodes that are coated on only one side of current collectors, stacks of such electrochemical cells, and methods of forming such electrochemical cell stacks.
Batteries are typically constructed of solid electrodes, separators, electrolyte, and ancillary components such as, for example, packaging, thermal management, cell balancing, consolidation of electrical current carriers into terminals, and/or other such components. The electrodes typically include active materials, conductive materials, binders and other additives.
Some known methods for preparing batteries include coating a metallic substrate (e.g., a current collector) with slurry composed of an active material, a conductive additive, and a binding agent dissolved or dispersed in a solvent, evaporating the solvent, and calendering the dried solid matrix to a specified thickness. The electrodes are then cut, packaged with other components, infiltrated with electrolyte and the entire package is then sealed.
Such known methods generally involve complicated and expensive manufacturing steps such as casting the electrode and are only suitable for electrodes of limited thickness, for example, less than 100 μm (final single sided coated thickness). These known methods for producing electrodes of limited thickness result in batteries with lower capacity, lower energy density and a high ratio of inactive components to active materials. Furthermore, the binders used in known electrode formulations can increase tortuosity and decrease the ionic conductivity of the electrode.
To increase the active material to inactive material ratio, conventional electrochemical cells are generally formed by coating the electrode active material (i.e., the anode formulation slurry and the cathode formulation slurry) on both sides of a current collector. A separator is disposed between the electrodes, i.e. the anode and cathode, to form a conventional electrochemical cell. A plurality of such electrochemical cells can be stacked on top of each other, generally with a spacer disposed therebetween, to form an electrochemical cell stack. While this positively impacts the active material to inactive material ratio, it introduces complications in the manufacturing process. Furthermore, the time required to assemble the electrochemical battery can be significant. This can increase the exposure of the electrode materials to temperature fluctuations or humidity which can degrade the electrode materials and thereby, the electronic properties of the electrodes.
Thus, it is an enduring goal of energy storage systems development to develop new electrochemical batteries and electrodes that have longer cycle life, increased energy density, charge capacity and overall performance.